Brake system and brake device for use with automobiles

ABSTRACT

A brake system and a brake device for use with automobiles is provided in which braking energy stored in an auxiliary pressure source can be effectively used for braking, even if an electrical system fails. The vehicle brake system includes a proportional pressure control valve for generating braking liquid pressure by adjusting the braking energy stored in the auxiliary pressure source. A passage transmits the liquid pressure generated by a brake pedal stroke, a switching valve opens the passage in the powered condition and closes the passage in the off-powered condition, and an auxiliary control portion activates the proportional pressure control valve. Even in the off-powered condition, the high pressure accumulated in the auxiliary pressure source can be used to adjust the required braking liquid pressure at the proportional pressure control valve.

This application is a continuation of U.S. patent application Ser. No.10/671,669, filed Sep. 29, 2003, which is a divisional of U.S. patentapplication Ser. No. 09/868,633, filed Sep. 10, 2001, now U.S. Pat. No.6,685,280, which was the National Stage of International Application No.PCT/JP00/07553, filed Oct. 27, 2000, the disclosures of which areexpressly incorporated herein by reference in their entireties. TheInternational Application was not published in English.

TECHNICAL FIELD

The present invention relates to a brake system preferably for use withautomobiles. In particular, the present invention relates to a brakesystem for automobiles, in which a braking substance or liquidpressurized by an auxiliary pressure source is adjusted and thensupplied for controlling a braking operation of wheels of the automobilein response to the brake stroke of the driver.

BACKGROUND ART

For the automobile brake system, with an increased development of acontrol system mounted on the automobile and a requirement of stabilityduring driving of an Anti-skid Brake System, referred to as “ABS”hereinafter, and a traction control, instead of a braking operation of adriving person, improved systems for the braking operation of the wheelsare available so that an electronic control system reads and thendetermines an optimal braking condition from the operation of thedriving person. Also, some of the systems are equipped with an auxiliarypressure source for the generation of a higher braking pressure inaddition to a mechanism for the generation of the braking pressure dueto a biasing force applied to a brake pedal by the driving person.

JP 10-86802 (A) discloses an example of the above-described brakesystem, in which a signal that indicates a braking pressure generated bythe braking operation of the driving person is transmitted to thecontroller. In response to the signal, the controller controls aseparate pressure generator so that the generator generates and thensupplies a braking liquid-pressure to the wheel systems. According tothe disclosed system, the liquid pressure generated by the brakingoperation of the driving person is used only for the generation of thecontrol signal but not used directly for the braking control of thewheel systems.

Also, JP 10-35455 (A) discloses another control system. According to thecontrol system, the braking force is calculated based upon a stroke ofthe pedal. A result of the calculation is then used for an adjustment ofa high pressure, generated by the auxiliary pressure source, at aproportional pressure control valve so that a suitably adjusted pressureis transmitted to the wheel systems. In this system, the liquid pressuregenerated by the pedal operation by the driving person is also used forthe braking operation of the wheels.

With reference to the drawings, a conventional brake system forautomobiles will be described below. FIG. 11 illustrates an example ofthe automobile brake system with an auxiliary pressure source. In thisdrawing, reference numeral 1 indicates a brake pedal on which thedriving person applies a biasing force for the brake control of theautomobile. Also, the reference numeral 2 indicates a device(hereinafter referred to a “master cylinder”) for generating a pressureforce in the braking substrate or liquid according to the brakingoperation of the driving person. For this purpose, the master cylinder 2is fluidly connected with two passages or tubes 3 and 4 to a reservoir 5for the accommodation of a braking substrate or liquid.

The master cylinder 2, which is a tandem cylinder with two pistonsarranged in a serial fashion within a cylinder, is capable of providingthe pressurized liquid in two ways or passages 6 and 16 fluidlyconnected at respective ends to respective pistons. The passage 6 isfluidly connected to a switching valve 7 and then branched into twosub-passages 8 and 9. Normally, an electromagnetic valve is preferablyused for the valve 7, although another type of valve may be employedinstead. The branched passage 8 is fluidly connected with a right-frontbrake unit 10 and the other branched passage 9 is fluidly connected witha left-rear brake unit 11, for example. When the electromagnetic valve 7is electrically disconnected from a power source, it is fluidlyconnected with the passage at its portion, e.g., left portion indicatedby an arrow with arrowheads at its opposite ends in the drawing,allowing the liquid in the passage 6 to pass therethrough. On the otherhand, when the electromagnetic valve 7 is electrically connected withthe power source, it is connected with the passage at its anotherportion, e.g., right portion, prohibiting the liquid in the passage 6from passing therethrough. Also, sensors 13 and 14 for sensing apressure of the liquid in the passage 6 are provided in the passage 6and on the opposite sides of the valve 7.

Likewise, the passage 16 is connected to an electromagnetic valve 17 andthen branched into sub-passages 18 and 19 which are in turn connectedwith left-front brake unit 20 and right-rear brake unit 21,respectively. The electromagnetic valve 17 has the same structure andconnection as those of the valve 7. Also, sensors 23 and 24 are arrangedon opposite sides of the valve 17 for the sensing of the pressure in theliquid passing therethrough. Further, although the automobile brakesystem includes other passages and valves for ABS and traction control,they are eliminated from the drawing for clarity.

In operation of the brake system so constructed, in the state shown inFIG. 11 when the valves are electrically disconnected from the powersource, the displacement of the pedal 1 due to the biasing operation ofthe driving person pressurizes the braking liquid accommodated in thetwo pistons in the master cylinder 2, which increases the pressure inthe passages. The pressure in the passage 6 is transmitted through theelectromagnetic valve 7 and then the passages 8 and 9 into brake unitsin the right-front and left-rear wheel units 10 and 11, respectively,where it is used for the braking control of respective wheels. Likewise,the pressure in the passage 16 is transmitted through theelectromagnetic valve 17 and passages 18 and 19 into brake units in theleft-front and right-rear wheel units 20 and 21, respectively, where itis used for the braking control of respective wheels.

Afterwards, when the biasing force is removed from the brake pedal, thepressure is removed from the pistons in the master cylinder 2. This alsoremoves the pressure in the passages 6 and 16, which releases the wheelsfrom the braking control thereof.

Descriptions will be made to other parts including an auxiliary pressuresource of the brake system. The auxiliary pressure source generallyindicated by reference numeral 30 includes a motor 31 with an outputshaft connected with two pumps 32. Each pump 32 is fluidly connected atan inlet or suction port thereof through a passage 34 to the reservoir 5and at an outlet or discharge port through a passage 35 to anaccumulator 36 and a sensor 37 for sensing the pressure in the passage.A relief valve 38 is provided for the protection of a disadvantageousrapid increase in pressure within the passages. Also, the passage 35 isfluidly connected to an input port 41 of a proportional pressure controlvalve 40 which will be described below. The valve 40 has output andreturn ports 42 and 44 connected with passages 43 and 45, respectively.The passage 45 is branched from the passage 34 and then terminates atthe reservoir 5.

The passage 43 connected at its one end to the output port 42 of thevalve 40 is branched into a passage 46 which is extended through anelectromagnetic valve 47 to the passages 8 and 9, and another passage 48which is extended through an electromagnetic valve 49 to the passage 18and 19. In the drawing, the electromagnetic valve 47 is illustrated tobe closed when it is disconnected from the power source. An electroniccontrol device 70 is provided so that it is electrically connected atits terminal indicated by alphabet A to terminals of the motor 31 andthe valve 40, also indicated by alphabet A. For clarity, the connectionsthereof are eliminated from the drawing. In addition, although notillustrated in the drawing, the control device 70 is electricallyconnected to all of the sensors 13, 14, 23, 24 and 37 and theelectromagnetic valves 7, 17, 47 and 49.

The operation of the auxiliary pressure source 30 and portions relatedthereto so constructed will be described hereinbelow. Upon rotation ofthe motor 31, the pumps 32 are driven to draw the brake liquid from thereservoir 5 through the passage 34 into the accumulator 36. Theaccumulator 36 may be selected from various types of accumulators. Forexample, if the piston type accumulator which is made of cylindricaltube with two spring-biased pistons received therein is used, the brakeliquid is forced in the accumulator 36 so that the springs arecompressed to accumulate the braking force or energy therein. Theadjacent pressure sensor 37 senses the braking pressure in theaccumulator 36. Then, when the pressure has reached a predeterminedvalue, the sensor 37 transmits a corresponding signal. The signal isthen transmitted to the control device 70, which in turn de-energizesthe motor 31.

The accumulated pressure decreases by the braking operations, which issensed by the pressure sensor 37. When the pressure sensor 37 detectsthat the pressure has decreased to a predetermined value, it transmits asignal to the control device 70. Upon receiving the signal, the controldevice 70 drives the motor 31 to accumulate the pressure in theauxiliary pressure source 30. This means that the auxiliary pressuresource 30 drives the pumps in response to the pressure decrease so thata certain amount of braking energy with the predetermined pressure isalways accumulated therein whenever the automobile is electricallypowered. The operation of the brake pedal 1 is not directly linked withthe pump 32. This ensures that, even when the electric system in theautomobile is disabled suddenly during driving, the auxiliary pressuresource maintains therein a sufficient braking energy.

The pressure of the brake liquid is transmitted through the passage 35to the input port 41 of the proportional pressure control valve 40.Then, by a control operation described below, the pressure is furthertransmitted through the output port 42 to the passage 43 and thenbranched passages 46 and 48 into the electromagnetic valves 47 and 49.While electrically disconnected from the power source as shown in FIG.11, the electromagnetic valves 47 and 49 close and the electromagneticvalves 7 and 17 open, which allows the braking pressure to betransmitted through the master cylinder 2 to the control device. Onceelectrically connected with the power source, the electromagnetic valves47 and 49 open and the electromagnetic valves 7 and 17 close. Thisallows the pressure of the braking liquid to be transmitted from thevalve 47 through the passages 8 and 9 to the brake units of theright-front and left-rear wheels 10 and 11, and from the valve 49through the passages 18 and 19 to the brake units of the left-front andright-rear wheels 20 and 21, respectively. This results in the fourwheels being well braked. In this braking operation, the brake liquid isaccumulated in the auxiliary pressure source 30 with an increasedpressure that is higher than that transmitted directly from the mastercylinder 2. This results in a greater braking force with less forceapplied on the pedal by the driver.

While connected with the power source, although not shown, theelectromagnetic valves 7 and 17 provided in the respective passages 6and 16 that connect the master cylinder 2 to the respective wheels areclosed. This prevents the pressure generated in the master cylinder dueto the biasing operation of brake pedal 1 from being transmitted to thewheels. When the system is electrically connected with the power source,a signal indicating the pressure in the master cylinder 2 is transmittedthrough the output terminals of the pressure sensors 13 and 23 to thecontrol device 70. Once received, the control device 70 calculates abrake force required for the braking of the wheels in response to theinput signal. Then, based upon the calculated brake force, the controldevice 70 transmits a signal to the valve 40 where the output pressurefrom the auxiliary pressure source 30 is adjusted to a certain levelsuitable for the braking control of respective wheels.

When an ignition of the automobile is turned off or the electric systemthereof is in a malfunction condition due to any reason, all of theelectromagnetic valves are turned off as illustrated in the drawing. Inthis instance, the breaking pressure caused by the braking operation ofthe pedal by the driving person is directly transmitted to the wheels10, 11, 20 and 21. Therefore, although the high pressure in theauxiliary pressure source 30 is not used for the braking operation, aminimum braking force required during the emergency is ensured.

FIG. 12 illustrates an example of the proportional pressure controlvalve 40 and portions related thereto. It should be noted that likeparts are denoted by like reference numerals throughout the drawings.Also, in this drawing, although the automobile has a plurality of wheelsand brake systems therefor as shown in FIG. 11, only one wheel and itsbrake system is illustrated therein for clarity. Likewise, the sensorsare also eliminated from the drawing.

In this drawing, the proportional pressure control valve 40 has anactuating or mechanical portion 50 and a control portion 60 indicated asupper and lower portions in the drawing, respectively. The mechanicalportion 50 includes a sleeve 51 in the form of a cylinder which isclosed at its uppermost end and opened at its lowermost end, and a spool52 mounted in an interior of the sleeve 51 so that it can move in anaxial direction of the sleeve 51 while making a sealing contact with aninner surface of the sleeve 51. The sleeve 51 has three ports; inputport 41, output port 42 and return port 44, formed therein so that eachof three ports fluidly communicates between interior and exteriorthereof. As described above, the three ports are connected with firstends of the passages 35, 43 and 45, respectively.

The spool 52 is formed at its mid portion in the longitudinal directionwith a reduced portion 53 which serves as a valve that connects anddisconnects between the input port 41 and the return port 44 by adisplacement of the spool 52 in the axial direction. The output port 42communicates with a chamber defined adjacent to the reduced portion 53irrespective of the position of the spool 52. The reduced portion 53 hasa transverse hole 54 that extends in a direction perpendicular to andcrossing the axial direction of the spool 52. The transverse hole 54 isfluidly connected with a vertical hole 55 that extends downwardly alongthe axial direction so that the holes 54 and 55 cooperate with eachother to form a T-shaped passage in the spool 52. The vertical hole 55receives a cylindrical pin 56 so that the pin moves in the axialdirection with a sealing contact between an outer surface of the pin andan inner surface of the vertical hole.

The control portion 60, which is mounted in the lower part of the valve40 and positioned in a coaxial fashion with the mechanical portion 50,has an outer cylindrical portion 61. The cylindrical portion 61 isclosed at its lower end that defines one end of the valve 40 and isopened at its upper end that makes a sealing connection with the bottomend of the sleeve 51. An inner diameter of the cylindrical portion 61 isgreater than that of the sleeve 51 to form a step at the connectionthereof. A coil 62 is wounded around the cylindrical portion 61. Also,provided in the interior of the cylindrical portion 61 is a stop 63 inthe form of rod that extends along the axial direction from the bottomend 64. Also, the top end of the stop 63 received the bottom end of thepin 56 to restrict a downward movement of the pin 56.

The spool 52 is formed at its bottom portion with an enlargedcylindrical portion 57 that extends downwardly in the interior of thecylindrical portion 61. The enlarged portion 57 cooperates with aportion of the spool 52 to define a step at an uppermost end of theenlarged portion. The step cooperates with another step formed betweenthe sleeve 51 and the cylindrical portion 61 to define a stoptherebetween that restricts an upward movement of the spool 52 and theenlarged portion 57. The enlarged portion 57 is formed from its bottomend with a hole that receives the rod-like stop 63. Also, the enlargedportion 57 is formed at its inner periphery surface with a step. Aspring 65 is supported at its opposite ends by the step and the closedend of the cylindrical portion 61 so that it forces the spool 52 upward.

An operation of the proportional pressure valve 40 so constructed willbe described hereinbelow. It should be noted that FIG. 12 is in partdifferent from FIG. 11 and illustrates a powered condition, i.e., inwhich the ignition key is turned on. In this state, upon operation ofthe brake pedal 1 by the driver, the master cylinder generates a brakingpressure that is transmitted to the passage 6. However, since theelectromagnetic valve 7 is closed as shown in the powered condition, thepressure is never transmitted directly to the wheel 10. A signalindicative of the pressure in the master cylinder 2 is transmitted fromthe pressure sensor 13 to the control device 70. Based upon the signal,the control device 70 calculates a required braking pressure and theninstructs the control 60 of the valve 40 to apply an electric currentnecessary for generating the required braking pressure. The coil 62cooperates with the enlarged portion 57 of the spool 52 to form asolenoid, so that the enlarged portion 57 is attracted to a magneticfield generated by the application of the electric current to the coil62. This causes the enlarged portion 57 together with the spool 52 tomove downward against the biasing force by the spring 65.

With the downward movement of the spool 52, the return port 44communicated with the reduced portion 53 is closed and then the inputport 41 is brought into communication with the reduced portion 53. Sincethe input port 41 is connected through the passage 35 with theaccumulator 36 for accumulating the brake liquid pressurized by thedriving of the pump 32, the communication between the input port 41 andthe reduced portion 53 allows the pressurized liquid to be fed from thepassage 35 through the input port 41 and the peripheral chamber definedby the reduced portion 53 to the output port 42. Then, the liquid is fedthrough the electromagnetic valve 49 that is opened in the poweredcondition and through the passages 43 and 48 to the wheel 10.

When the brake pedal 1 is released by the driver, the pressure in themaster cylinder 2 decreases, which is transmitted from the pressuresensor 13 to the control device 70. Then, the control device 70 turnsoff the application of the electric current to the coil 62. Thisde-energizes the solenoid to cause the spool 52 to move upward due tothe force applied thereto by the spring 65. At this moment, the inputport 41 is closed to prohibit the braking liquid from flowing into thereduced portion 53. Instead, the reduced portion 53 is connected to thereturn valve 44, which causes the braking pressure that has been appliedto the wheel 10 to be released through the output port 42 into thereturn port 44.

Another description will be provided of a relationship between thedisplacement of the brake pedal and the braking pressure liquidpressure. As described above, the signal indicative of the pressure inthe master cylinder 2, caused by the stroke of the brake pedal, istransmitted from the pressure sensor 13 to the control device 70. Inresponse to the signal, the control device 70 instructs the valvecontrol 60 of the proportional pressure control valve 40 to apply theelectric current I that is proportional to the braking pressure.Typically, it has been known that the force for the solenoid to move thespool varies in proportion to the square of the current.

As described above, the spool 52 includes the transverse hole 54 and avertical hole 55 in which the pin 56 is inserted. The lowermost end ofthe pin 56 is exposed to the interior of the cylindrical portion 61where no braking pressure applies thereto. This means that an excessivepressure (P×S) acts in the transverse hole 54, wherein

-   P: Braking pressure introduced through input port 41;-   S: Cross section of pin 56 (corresponding to cross section of    vertical hole 55); and-   F: Biasing force upwardly applied to the spool 52 by the spring 65.    This results in that the spool 52 stays where an upward force that    is the sum of the upward force (P×S) and the biasing force F of    spring 65 balances to a downward force caused by the coil 61. This    balanced state can be indicated by the following equation:    P×S+F=a×I ² (a: Coefficient)    This can be written as follows:    P=[a×I ² −F]/S

This relation, which is graphed as shown in FIG. 13, means that thebraking pressure is proportional to the square of the current or thebiasing force applied to the brake pedal. This further means that theproportional pressure valve 40 uses the high braking pressureaccumulated in the accumulator 36 in order to adjust the requiredbraking pressure to be transmitted to the wheel, depending upon thestroke of the brake pedal.

FIG. 14 illustrates another conventional brake system. The system doesnot include means for transmitting the liquid pressure in the mastercylinder 2, generated by the operation of brake pedal 1, to the wheel 10directly. Alternatively, a signal indicative of the pressure in theliquid is transmitted to the control device 70. Then, a requiredpressure for braking is generated only by the operation of the valve 40driven by the instruction from the control device 70.

As shown, the master cylinder 2 has a pressure sensor 13 fortransmitting a signal indicative of the pressure to the control device70. Also, the braking pressure to be used for braking the wheel 10 isobtained only from the proportional pressure control valve 40. Thisallows the electromagnetic valve for changing the passages to beeliminated, which simplifies the structure of the brake system. Otherparts are the same as those described above and, therefore, no detaileddescription will be made thereto. With the arrangement, indeed thestructure of the brake system can be simplified. However, since no meansis included for applying a certain braking pressure to the wheels, aseparate structure should be provided for safety during possibleemergencies, such as any failure of the electric system.

As described above, for the conventional brake system, the pressureaccumulated in the auxiliary pressure source is not used for the brakingoperation during emergencies caused by, for example, the electric orsystem failure in the automobile. That is, in the conventional brakesystem disclosed in JP 10-86802 (A), although the pressurized liquid isaccumulated in the auxiliary pressure source, it is prohibited by theelectromagnetic valve from being transmitted to the wheels duringelectric failure. Also, the pressure generated by the pedal operation isnot transmitted to the wheels, which disadvantageously brings theautomobile into a condition in which no braking pressure is applied tothe wheels. To prevent this, another auxiliary brake system should beprovided.

On the other hand, the brake system disclosed in JP 10-35455 (A) isdesigned so that the pressure in the liquid generated by the operationof the brake pedal is transmitted to the wheels even during emergenciesin which no electric power is supplied to the brake system. This ensuresa certain braking force, although it might be a minimum braking pressurecaused by the driver, that must be ensured by the manufactures. Duringelectric system failure, the pressure accumulated in the auxiliarypressure source is prevented by the electromagnetic valve from beingtransmitted to the wheels. This means that the pressure is not usedeffectively for the braking during emergencies.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a brake system forautomobiles, which is capable of exploiting the braking energy,accumulated in the auxiliary pressure source, not only under the normalcondition but also during emergencies such as electric or system failurethereof.

In order to address the aforementioned problems, the brake system of thepresent invention includes an auxiliary control means for activating aproportional pressure control valve even in emergency such as in amalfunction of an electrical failure. Alternatively, the auxiliarycontrol means actuates the proportional pressure control valve inaccordance with a stroke of the brake pedal for generating higherpressure. The braking energy stored in the auxiliary pressure source istransmitted to each wheel for generating sufficient braking force.Details will be discussed hereinafter.

One aspect of the present invention relates to a brake system for usewith automobiles, including: signal generating means for generating asignal in response to a stroke of a brake pedal; pressurized liquidaccumulating means for pressuring a braking liquid and storing the sametherein; proportional pressure control means for adjusting the pressureof the braking liquid in accordance with the signal output from thesignal generating means, and for transmitting the adjusted pressure ofthe braking liquid to the wheels; and auxiliary control means forcontrolling the proportional pressure control means while electricallydisconnected with a power source so that the pressurized braking liquidprovided through the proportional pressure control means can be used asa braking force. Thus, the pressurized braking liquid stored in thepressurized liquid accumulating means can be exploited for obtaining aneffective braking force even in the off-powered condition.

Another aspect of the present invention relates to a brake system foruse with automobiles, including: signal generating means for generatinga signal in response to a stroke of a brake pedal; pressurized liquidaccumulating means for pressuring a braking liquid and storing the sametherein; proportional pressure control means for adjusting the pressureof the braking liquid in accordance with the signal output from thesignal generating means, and for transmitting the adjusted pressure ofthe braking liquid to the wheels; and auxiliary control means forcontrolling the proportional pressure control means once the brake pedalis stepped beyond a predetermined stroke; wherein the proportionalpressure control means is controlled both by the signal output from thesignal generating means and by the auxiliary control means so that thepressurized braking liquid provided through the proportional pressurecontrol means can be used as a braking force. Thus, the operation of thebrake pedal can activate the proportional pressure control means even inthe on-powered and off-powered conditions.

Even another aspect of the present invention relates to a brake systemfor use with automobiles, in which the auxiliary control means actuatesthe proportional pressure control means in accordance with the pressureof the braking liquid generated by the stroke stepped by the driver.Also, the auxiliary control means may actuate the proportional pressurecontrol means through an elastic member in accordance with the pressureof the braking liquid generated by the stroke stepped by the driver.

Even another aspect of the present invention relates to a brake systemfor use with automobiles, in which the auxiliary control means has amoving portion engaging with the brake pedal, the moving portiondirectly actuating the proportional pressure control means in accordancewith the stroke stepped by the driver. Also, the auxiliary control meansmay have a moving portion engaging with the brake pedal, the movingportion directly actuating the proportional pressure control meansthrough an elastic member in accordance with the stroke stepped by thedriver.

Even another aspect of the present invention relates to a brake systemfor use with automobiles, including: a master cylinder for generating apressure of a braking liquid in response to a stroke of a brake pedal; aliquid pressure sensor for detecting the pressure of the braking liquidwithin the master cylinder; a reservoir for storing the braking liquid;an auxiliary pressure source for pressurizing the brake liquid withinthe reservoir and for accumulating the pressurized braking liquid; acontroller for calculating a braking liquid pressure required forbraking wheels, based upon information output from the liquid pressuresensor; a proportional pressure control valve for adjusting thepressurized braking liquid in accordance with an electric signal outputfrom the controller; a passage for communicating the braking liquidwithin the master cylinder to the proportional pressure control valve; aswitching valve intervened in the passage for communicating the brakingliquid while electrically disconnected with a power source and forblocking the same while electrically connected with the power source;and an auxiliary control mechanism for causing the proportional pressurecontrol valve to adjust the braking liquid pressure pressurized by theauxiliary pressure source in accordance with the pressure transmittedfrom the master cylinder. To this end, in the vehicle brake system,which does not transmit the liquid pressure within the master cylinderdirectly to the wheels, the sufficient braking force can be obtained inthe off-powered condition.

Instead of the switching valve intervened in the passage, a relief andreturn valves can be used. The relief valve transmits the braking liquidwithin the master cylinder, if the pressure of the braking liquid isexceeding over a predetermined value. The return valve returns thebraking liquid from the proportional pressure control valve to themaster cylinder, if the pressure of the braking liquid is released.Thus, the operation of the brake pedal can activate the proportionalpressure control valve even in the on-powered and off-poweredconditions.

Even another aspect of the present invention relates to a brake systemfor use with automobiles, including: a master cylinder for generating apressure of a braking liquid in response to a stroke of a brake pedal; aliquid pressure sensor for detecting the pressure of the braking liquidwithin the master cylinder; a first passage for transmitting thepressure of the braking liquid within the master cylinder to wheels; afirst switching valve intervened in the first passage, for transmittingthe pressure of the braking liquid within the master cylinder to wheelswhile electrically disconnected with a power source, and for blockingthe same while electrically connected with the power source; a reservoirstoring the braking liquid; an auxiliary pressure source forpressurizing the braking liquid within the reservoir and foraccumulating the pressurized brake liquid; a controller for calculatinga braking liquid pressure required for braking wheels, based uponinformation output from the liquid pressure sensor; a proportionalpressure control valve for adjusting the pressurized braking liquid inaccordance with an electric signal output from the controller; a secondpassage for communicating the pressurized braking liquid adjusted by theproportional pressure control valve to wheels; a second switching valveintervened in the second passage, for transmitting the pressurizedbraking liquid adjusted by the proportional pressure control valve tothe wheels, while electrically connected with the power source, and forblocking the same while electrically disconnected with the power source;a third passage for communicating the braking liquid within the mastercylinder to the proportional pressure control valve; a third switchingvalve intervened in the third passage, for transmitting the brakingliquid within the master cylinder to the proportional pressure controlvalve, while electrically connected with the power source, and forblocking the same while electrically disconnected with the power source;an auxiliary control mechanism for causing the proportional pressurecontrol valve to adjust the braking liquid pressure pressurized by theauxiliary pressure source in accordance with the pressure transmittedfrom the master cylinder through the third passage to the proportionalpressure control valve; a fourth passage for bypassing the secondswitching valve selectively transmitting and blocking the secondpassage; and a booster piston intervened in the fourth passage, whilethe second switching valve blocks the second passage and the pressurizedbraking liquid adjusted by the proportional pressure control valve istransmitted to the fourth passage, for blocking the first passage thatcommunicates the braking liquid within the master to the wheels, and forpressurizing the braking liquid applied to the wheels. To this end, inthe vehicle brake system, which transmit the liquid pressure within themaster cylinder directly to the wheels, the pressurized braking liquidstored in the accumulator can be used so that the sufficient brakingforce can be obtained even in the off-powered condition.

Instead of the third switching valve intervened in the third passage, arelief and return valves can be used. The relief valve transmits thebraking liquid within the master cylinder, if the pressure of thebraking liquid is exceeding over a predetermined value. The return valvereturns the braking liquid from the proportional pressure control valveto the master cylinder, if the pressure of the braking liquid isreleased. Thus, the operation of the brake pedal can activate theproportional pressure control valve even in the on-powered andoff-powered conditions.

Even another aspect of the present invention relates to a brake systemfor use with automobiles, in which instead of, or in combination withthe liquid pressure sensor, a stroke sensor is provided for detectingthe stroke of the brake pedal, and the controller calculates the brakingliquid pressure required for braking wheels, based upon informationoutput from the stroke sensor, instead of, or in combination withinformation output from the liquid pressure sensor. The more suitablebraking operation can be realized.

Even another aspect of the present invention relates to a brake systemfor use with automobiles, including: a stroke sensor for detecting astroke of a brake pedal; a reservoir for storing a braking liquid; anauxiliary pressure source for pressurizing the brake liquid within thereservoir and for accumulating the pressurized braking liquid; acontroller for calculating a braking liquid pressure required forbraking wheels, based upon information output from the stroke sensor; aproportional pressure control valve for adjusting the pressurizedbraking liquid supplied from the auxiliary pressure source in accordancewith an electric signal output from the controller; and an auxiliarycontrol mechanism including a moving portion engaging with the brakepedal, the moving portion directly actuating the proportional pressurecontrol mechanism in accordance with the stroke, if the brake pedal isstepped beyond a predetermined stroke. Thus, the operation of the brakepedal can mechanically control the proportional pressure control valveeven in the on-powered and off-powered conditions.

Even another aspect of the present invention relates to a brake systemfor use with automobiles, in which the auxiliary control mechanismincludes a push rod positioned with the brake pedal that opposes to aspool switching the proportional pressure control valve or an extensionportion thereof with a predetermined gap therebetween, and the push rodcontacts with the spool or extension portion thereof after the brakepedal is stepped beyond a predetermined stroke, and presses it. Also,the spool, the extension rod, or the push rod may be partially made ofelastic material, and the elastic material may be a spring.

Even another aspect of the present invention relates to a brake systemfor use with automobiles, in which the auxiliary control mechanismincludes an extension rod extending from a spool switching theproportional pressure control valve, and an electromagnetic clutchinstalled with the extension rod, and upon receiving a signal indicatingthat the brake pedal is stepped beyond a predetermined stroke, theelectromagnet clutch holds the extension rod so as to press the spoolthrough the extension rod.

Even another aspect of the present invention relates to a brake systemfor use with automobiles, including: a stroke sensor for detecting astroke of a brake pedal; a reservoir for storing a braking liquid; anauxiliary pressure source for pressurizing the brake liquid within thereservoir and for accumulating the pressurized braking liquid; acontroller for calculating a braking liquid pressure required forbraking wheels, based upon information output from the stroke sensor; aproportional pressure control valve for adjusting the pressurizedbraking liquid supplied from the auxiliary pressure source in accordancewith an electric signal output from the controller; and an auxiliarycontrol mechanism including a moving portion engaging with the brakepedal, the moving portion directly actuating the proportional pressurecontrol mechanism in accordance with the stroke, while electricallydisconnected with a power source.

Even another aspect of the present invention relates to a brake systemfor use with automobiles, in which the auxiliary control mechanismincludes an extension rod extending from a spool switching theproportional pressure control valve, and an electromagnetic clutchinstalled with the extension rod, and the electromagnet clutch holds theextension rod so as to press the spool through the extension rod, whileelectrically disconnected with a power source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of the preferred embodiment of abrake system for use of automobiles according to the present invention.

FIG. 2 is a partial schematic view of the brake system in FIG. 1,illustrating a proportional pressure control valve in detail.

FIG. 3 is another partial schematic view of the brake system in FIG. 2,illustrating a proportional pressure control valve in detail.

FIG. 4 is a partial schematic view of another preferred embodiment ofthe brake system illustrating a proportional pressure control valve indetail.

FIG. 5 is a partial schematic view of another preferred embodiment ofthe brake system illustrating a proportional pressure control valve indetail.

FIG. 6 is a partial schematic view of another preferred embodiment ofthe brake system illustrating a proportional pressure control valve indetail.

FIGS. 7( a) and 7(b) are partial schematic views of modifications of thealternative embodiment shown in FIG. 6.

FIG. 8 is a partial schematic view of another preferred embodiment ofthe brake system illustrating a proportional pressure control valve indetail.

FIGS. 9( a) and 9(b) are partial schematic views of modifications of thealternative embodiment shown in FIG. 8.

FIG. 10 is a graph illustrating a relationship between a stroke of abrake pedal and a pressure of a braking liquid.

FIG. 11 is a schematic block diagram of a prior art brake system for usewith automobiles.

FIG. 12 is a partial schematic view of the brake system shown in FIG.11.

FIG. 13 is a graph illustrating a relationship between a currentprovided in a coil of the proportional pressure control valve and apressure of a braking liquid.

FIG. 14 is a schematic block diagram of another prior art brake systemfor use with automobiles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawings, a first preferred embodiment of a brakesystem for automobiles according to the present invention will bedescribed in detail. FIG. 1 illustrates a brake system for automobilesaccording to an embodiment of the present invention, which includesadditional components added to the conventional brake system describedabove and illustrated in FIG. 11. In the drawing, added is a passage 75that connects between the master cylinder 2 and the proportionalpressure control valve 80 and includes an electromagnetic valve 76intervened therein. While the brake system is not applied with anelectric power, the electromagnetic valve 76 is opened so that pressurein the master cylinder 2 is transmitted to the valve 80 as shown in thedrawing. The valve 80 has additional features that are not provided inthe conventional proportional pressure control valve 40, which will bedescribed hereinafter.

Booster pistons 90 and 100 are positioned and fluidly connected betweenthe passages (higher pressure passages) 43 and 46 extended from theauxiliary pressure source and the passages (lower pressure passages) 6and 16 extended from the master cylinder 2, respectively. This allowsthe higher pressure and lower pressure passages to be connected anddisconnected so that the braking pressure applied to the braking unitsfor the wheels to be increased, which will be described in detailhereinafter. An optional stroke sensor 120 is provided so that it sensesthe stroke of the pedal 1 stepped by the driver.

FIG. 2 illustrates a structure of the proportional pressure controlvalve 80 and portions related thereto. For clarity, there is shown onlya part, i.e., one unit of the brake system and one wheel relatedthereto, and other portions such as sensors are eliminated therefrom,although the brake system of the present invention has four units forrespective wheels and sensors as illustrated in FIG. 1. Comparing withthe proportional pressure control valve 40, the proportional pressurecontrol valve 80 according to the present invention includes anauxiliary control portion 81 in addition to the mechanical portion 50and the control portion 60 provided in the conventional valve.

The auxiliary control portion 81 has a casing 82 made from a hollowcylindrical member closed at opposite longitudinal end walls thereof.One closed end wall of the casing 82 is fixedly and tightly connected tothe upper end portion of the mechanical portion 50 in a coaxial fashiontherewith. The other closed end wall of the casing 82 defines one end,i.e., topmost end in the drawing, of the proportional pressure controlvalve 80. Provided within the casing 82 is an auxiliary piston 84, whichhas a flange 83 at its one end thereof and extends from an interior ofthe casing through a hole formed in the lowermost end wall of the casing82 to the exterior of the casing 82 adjacent to the top end of the spool52 at its other end. A sealing ring such as an O-ring 85 is providedaround the auxiliary piston 84 and in the through-hole so that theauxiliary piston 84 is sealingly and movably supported in thethrough-hole. A biasing member such as helical spring 86 is providedbetween the flange 83 and the lower end wall of the casing 82, adjacentto the mechanical portion 50, so that the auxiliary piston 84 is biasedupwardly. Although not shown, the auxiliary piston 84 is formed at itsperiphery, below the bottom end wall of the casing 82, with a peripheralcutouts or groove in which a stop such as E-ring is engaged in order toprevent the piston 84 from being pulled out of the through-hole into theinterior of the casing 82.

The casing 82 has a pressure control port 87 formed therein to which oneend of the passage 75 is fluidly connected so that the interior of thecasing 82 is fluidly connected through the electromagnetic valve 76 withthe master cylinder 2. In the powered condition shown in FIG. 2, theelectromagnetic valve 76 is closed so that, in the normal drivingcondition, the auxiliary control portion 81 does not cooperate with thebraking operation. Other portions of the valve 80 including themechanical portion 50 and the control portion 60 functions as describedabove irrespective of the auxiliary control portion 81.

Next, an operation of the proportional pressure control valve 80 soconstructed will be described. As in the conventional brake system, anyelectric failure of the brake system disconnects the coil 62 of thecontrol portion 60 in the proportional pressure control valve 80 fromthe power source, which results in the malfunction of the proportionalpressure control valve 80. This further results in the sufficientbraking energy that is accumulated in the accumulator 36 not beingavailable for the braking control. Notwithstanding, since theelectromagnetic valves 7 and 76 are switched open so that the liquidpressure of the master cylinder 2 is transmitted through theelectromagnetic valve 7 to the wheel 10, the minimum braking control canbe assured.

In the proportional pressure control valve 80 of the present invention,the disconnection of power to the additional electromagnetic valve 76makes the valve open so that the liquid pressure of the master cylinder2 is transmitted through the passage 75 and the pressure control port 87into the casing 82 of the auxiliary control portion 81. Theabove-mentioned auxiliary piston 84 is provided in the casing 82. Theflange 83 of the auxiliary piston 84 receives the liquid pressure acrossan upper surface thereof. Also, the lower surface of the flange 83 isconnected with one end of the auxiliary piston 84, of which other end isexposed outside the casing 82. Therefore, the pressure corresponding tothe cross-sectional area of the auxiliary piston 84 is applied to theflange 83 in the direction from the top to the bottom, i.e., downwardlyin the drawing. Thus, the auxiliary piston 84 is pressed down againstthe biasing force of the spring 86.

Since the lowermost end of the auxiliary piston 84 is close to or incontact with the uppermost end of the spool 52 of the proportionalpressure control valve 80, the downward movement of the auxiliary piston84 presses down the spool 52 against the biasing force. Eventually, thechannel defined by the reduced portion 53 of the spool 52 fluidlycommunicates with the input port 41 so that the pressurized brakingliquid stored in the accumulator 36 is transmitted to the passage 43through the input port 41, the reduced portion 53, and the output port42. Meantime, the electromagnet valve 49 is switched to the closedposition from the open position illustrated in the drawing. Thus, thepressure of the braking liquid is transmitted to an additional componentof the present invention, i.e., a booster piston 90.

FIG. 3 is a schematic view illustrating the structure of the boosterpiston 90 and other related components thereof. Contrary to FIG. 2, FIG.3 shows the off-powered condition where the electric system is notsupplied with the electric power. The booster piston 90 includes a pairof overlapping hollow cylindrical members having both closed ends in theaxial direction, in which the outer cylindrical member is a cylinder 91and the inner is a piston 92. The piston 92 is arranged in the cylinder91 with sealing contact therebetween so that the piston 92 can slide inthe axial direction. The piston 92 has a through-hole 93 on one endthereof, through which a needle valve 94 extends from the inside of thepiston 92. Also, the needle valve 94 is biased towards the through-hole93 by a spring 96 arranged between the other end of the piston 92 and aninside end of the needle valve 94. Also, an another spring 98 arrangedbetween the left end 97 of the cylinder 91 opposing to the needle valve94 and the left end of the piston 92 biases the piston 92 towards adirection (from the left to the right in the drawing), where the needlevalve is pressed down so as to open the valve.

A port 99 serving also as a valve seat is provided on the center of theleft end 97 of the cylinder 91, opposing to the needle valve 94. Theport 99 is fluidly connected with the passage 6 in communication withthe master cylinder 2. Another port 101 is defined in the left end 97 ofthe cylinder 91 so as to connect the booster piston 90 with the wheel 10through the passage 6′. Also, defined in the right end of the cylinder91 opposing to the left end 97 is a port 102 fluidly connected with theoutput port 42 of the proportional pressure control valve 80.

Even if the electric system shuts down, usage of the booster piston 90so constructed in cooperation with the braking operation of the drivercauses the auxiliary control portion 81 illustrated in FIG. 2 toactivate the proportional pressure control valve 80. Thus, the highpressure of the braking liquid generated by the auxiliary pressuresource can be transmitted to the passage 43 through the output port 42.Then, because the electromagnetic valve 49 is closed, the high pressureis guided to the booster piston 90 bypassing the electromagnetic valve49. Thus, the high pressure of the braking liquid is transmitted throughthe port 102 of the booster piston 90 into the cylinder 91 so that,depending upon the difference between the pressures applied to the port99 and 102, the piston 92 moves towards the left direction in thedrawing to forward the needle valve 94 against the biasing force of thespring 98. To this end, the needle valve 94 closes the port 99 so as tostem the liquid in the passage 6 communicating between the mastercylinder 2 and wheel 10. The biasing force of the spring 96 keeps theport 99 closed. Further, the liquid pressure from the port 102 advancesthe piston 92, and then the braking liquid confined within the cylinder91 is pressurized, which is transmitted as the braking pressure throughthe port 101 and the passage 6′ to the brake system of the wheel 10 soas to generate the braking force.

If the high-pressurized braking liquid is not accumulated in theauxiliary pressure source, then the booster piston 90 is not activatedso that the needle valve 94 maintains the port 99 open. Therefore, thepassage 6 communicates with the passage 6′ through the port 99 and 101whereby the liquid pressure generated within the master cylinder 2 istransmitted directly to the wheel 10. According to the presentinvention, even if the electric system fails down, in case where thehigh-pressurized braking liquid is accumulated in the auxiliary pressuresource, the stepping force of the driver can activate the strongerbraking force with use of the high-pressurized braking liquid so as toensure safety in emergency, and also in a condition in which theaccumulated high pressure is not available, the minimum braking forcecan be ensured.

In the normal operation with the power supplied, the electromagnet valve49 is open. Thus, the pressures applied to between the port 99 and theport 101 are the same so that the piston 92 is maintained still and theport 101 is kept open. Therefore, in the normal operation, no passageconnecting with the booster piston 90 defines the bypassing passage ofthe electromagnet 49, and the booster piston 90 gives no contribution tothe operation of the system. All of the braking liquid pressures aretransmitted to the wheel 10.

Next, with reference to the drawings, a second preferred embodiment of abrake system for automobiles according to the present invention will bedescribed in detail. FIG. 4 is a schematic view of the brake systemaccording to an embodiment of the present invention, in which thepressure of the braking liquid is not transmitted directly from themaster cylinder 2 but exclusively from the proportional pressure controlvalve to the wheel 10. In the drawing, reference numeral 80 denotes theproportional pressure control valve including the auxiliary controlportion 81, in which the pressure control port 87 is connected with themaster cylinder through the passage 75 and the electromagnet valve 76.Because the structure of the auxiliary control portion 81 is the same asthat illustrated in the first embodiment, no further description will bemade. In the brake system of the embodiment, since the liquid pressureis transmitted to the wheel only through the proportional pressurecontrol valve 80, no electromagnetic valve is required for switching thepassage of the pressure. Thus the booster piston 90 serving as a bypassduring the electrical malfunction is also eliminated. To this end, thewhole structure of the system can be simplified.

Basically, the operation of the vehicle brake system so constructed issimilar to that of the first embodiment. In the normal operation (i.e.,in powered condition), the closure of the electromagnetic valve 76 asshown in the drawing does not activate the auxiliary control portion 81,the braking pressure is applied to the wheel 10 from the proportionalpressure control valve 80 that adjusts the pressure in response to theinstruction output from the control portion 70 to the valve controlportion 60 having the solenoid. Once the electric system of theautomobile fails due to any reasons, the electromagnetic valve 76 isopen so that the liquid pressure within the master cylinder 2 istransmitted to the auxiliary control portion 81 of the proportionalpressure control valve 80. Then, as described above, the auxiliarypiston 84 is pressed down to activate the proportional pressure controlvalve 80 so that the high pressure of the braking liquid stored in theaccumulator 36 is transmitted to the wheel 10. Adding the simplecomponent of the present invention to the brake system, which does notitself generate the braking force during the electric failure and has nofail-safe function, advantageously causes the brake system to generatethe usual braking force even in such emergency.

Next, with reference to the drawings, a third preferred embodiment of abrake system for automobiles according to the present invention will bedescribed in detail. FIG. 5 is a schematic view of the brake systemaccording to an embodiment of the present invention. The proportionalpressure control valve 110 of the embodiment is similar to theconventional one described above and illustrated in FIG. 14 except thatit is provided with an extension rod 111 extending from the uppermostend of the spool 52 via a through-hole 112 formed on the closed end ofthe sleeve 51, and with an O-ring 85 arranged within the through-hole112 for sealing the extension rod 111. The extension rod 111 is biasedby a spring 86, upwardly in the drawing. Also, a flange is positioned soas to prevent the extension rod from upwardly slipping off due to thebiasing force. An electromagnetic clutch 113 is provided with the brakepedal 1 for holding or releasing the extension rod 111. Theelectromagnetic clutch 113 of the embodiment is designed so that itreleases the extension rod 111 to set it free during the poweredcondition of the automobiles, and holds the extension rod 111 during theoff-powered condition. Although the stroke sensor 120 is provided withthe brake pedal 1, it is not limited thereto, and any other sensors suchas a combination of master cylinder 2 and the pressure sensor 13 and astepping force sensor may be utilized. Other structures of theembodiment are similar to those of the conventional vehicle brakingsystem illustrated in FIG. 14.

In operation of the brake system used for automobiles according to thepresent invention, the stroke of the brake pedal 1 stepped by the driveris detected by the stroke sensor 120. The stroke sensor 120 output asignal to the control device 70, which in turn, moves the proportionalpressure control valve 110 in response to the stroke. The movement ofthe proportional pressure control valve 110 leads the pressurizedbraking liquid therein so as to advantageously be used for braking thewheel. This operation is similar to that of the prior art.

In case where the automobile is disconnected from the power, theconventional proportional pressure control valve 40 is inoperable toexploit the high pressure of the braking liquid as described above.Contrary to this, according to the present invention, theelectromagnetic clutch 113 grasps or holds the extension rod 111 in theoff-powered condition. This causes the force applied to the brake pedal1 to be transmitted directly through the electromagnet clutch 113 to theextension rod 111. Then, the extension rod 111, in turn, presses thespool 52 downwardly so that the pressurized braking liquid stored withinthe accumulator 36 can be conducted into the input port 41. As above,the pressurized braking liquid can be used to ensure the braking forcesufficient for braking the wheel, even in the off-powered condition.

Although the embodiment of the present invention illustrated in FIG. 5is applied to the prior art brake system shown in FIG. 14, it is notlimited thereto, and it may also be applied to any types of vehiclebrake systems. Also, the extension rod 111 is indicated as a separatecomponent in FIG. 5, however, it may be formed integrally with the spool52 that extends upwardly through the sleeve 51 up to the electromagnetclutch 113 for holding or releasing an extending portion thereof. Tothis end, the provision of the simple component of the present inventionwith the brake system, which does not itself generate the braking forceduring the electric failure and has no fail-safe function,advantageously causes the brake system to generate the usual brakingforce even in such emergency.

Further, with reference to the drawings, a fourth preferred embodimentof a brake system for automobiles according to the present inventionwill be described in detail hereinafter. One of the objects of theforegoing embodiments is to exploit the high pressure of the brakingliquid stored in the accumulator sufficiently for braking the wheelswhile the electric system of the automobiles fails. In addition, whilethe electric system of the automobiles does not fail, i.e., in thepowered condition, the high pressure of the braking liquid can beapplied in response to the stroke of the brake pedal for effectivelybraking the wheels.

FIG. 6 illustrates the brake system for automobiles of the embodiment,which is similar to that of the second embodiment as described above andillustrated in FIG. 4, except that the electromagnet valve 76 intervenedin the passage, which communicates the master cylinder 2 and theproportional pressure control valve 80, is replaced with the reliefvalve 116 and the return valve 117 shown in FIG. 6. The replacement ofthe electromagnet valve 76 with the relief valve 116 and the returnvalve 117 causes the liquid pressure within the master cylinder 2 to betransmitted through the relief valve 116 to the auxiliary controlportion 81 in the normal powered operation mode. In particular, untilthe pressure of the braking liquid within the master cylinder 2overcomes the biasing force applied by a valve closing spring in therelief valve 116, the control device 70 adjusts the proportionalpressure control valve 80 in response to the signal output from theliquid pressure sensor 13 in the same manner as the conventional controldevice does. Meanwhile, once the pressure of the braking liquidovercomes the biasing force applied by a valve closing spring, it istransmitted through the passage 75 to the auxiliary control portion 81,which in turn, presses down the auxiliary piston 84 so as to actuate theproportional pressure control valve 80. To this end, the appliedpressure to the wheels is the pressure generated by the auxiliarycontrol portion 81, in addition to the pressure controlled by theproportional pressure control valve 80 in response to the signal outputfrom the liquid pressure sensor 13. Thus, the higher pressure can beapplied to the wheels.

The release of the brake pedal 1 by the driver reduces the pressure ofthe braking liquid within the master cylinder 2 so as to close therelief valve 116. The upward movement of the auxiliary piston 84 returnsthe redundant braking liquid to the master cylinder 2 through the returnvalve 117.

One of the advantages of the vehicle brake system according to theembodiment is, as described above, to obtain the higher pressure byincreasing the movement of the proportional pressure control valve 80when the stroke of the brake pedal exceeds beyond the predetermined onein normal powered condition. Therefore, for example, even if a gainoutput in response to the stroke of the brake pedal from the strokesensor or a gain output from the liquid pressure sensor is reducedbecause of any malfunctions, the higher pressure can be ensured forefficiently braking the wheels. Besides, even if the electric systemfails, the proportional pressure control valve 80 can be operated. Tothis end, the braking force is increased in the powered condition, andalso the safety is advantageously improved in emergency.

The embodiment of the present invention shown in FIG. 6 is applied tothe brake system described above and illustrated in FIG. 4, by thereplacement of the electromagnet valve 76 with the relief valve 116 andthe return valve 117. However, it is not limited thereto, and it mayalso be applied to any types of the brake systems as illustrated inFIGS. 1 and 2 by the replacement of the electromagnet valve 76 with therelief valve 116 and the return valve 117.

FIGS. 7( a) and 7(b) are partial views of modifications of theembodiment, illustrating only the modified portions of the vehicle brakesystem. The other structure is similar to that shown in FIG. 6. In FIG.7( a), the liquid pressure within the master cylinder 2, generated bythe brake pedal operation, is transmitted to the proportional pressurecontrol valve 110 through the relief valve 116 in a similar manner tothat illustrated in FIG. 6. The proportional pressure control valve 110has an inner bore, in which a plurality of springs 119 and anotherpiston 121 are installed on an upper surface of the spool 52. The liquidpressure applied to the piston 121 presses down the piston 121 againstthe biasing force of the springs 119. According to this modification,the advantage similar to that of the embodiment described above isobtained, also in addition, advantageously, the spring 119 serves as abuffer.

In the proportional pressure control valve 110 shown in FIG. 7( b), thesleeve 51 b has an enlarged bore portion, in which, in addition to theinstallation of the springs 119 and the piston 121 on the upper surfaceof the spool 52, other springs 122 are installed on a step defined bythe enlarged bore portion. The piston 122 is upwardly biased by thosesprings. At the initial step when the brake pedal 1 is stepped toincrease the pressure within the master cylinder 2, the increasedpressure is balanced with the biasing force by the springs 122. However,after the increased pressure is beyond the predetermined pressure, theanother springs 119 are also compressed downwardly so as to press downthe spool 52. The proportional pressure control valve 110 so constructedeliminates the relief valve 116 and the return valve 117 to simplify thestructure thereof. The operations in the powered and off-poweredconditions bring similar advantages to those illustrated in FIG. 7( a).

Next, with reference to the drawings, a fifth preferred embodiment of abrake system for automobiles according to the present invention will bedescribed in detail. FIG. 8 illustrates a brake system for automobilesaccording to an embodiment, which generally includes the proportionalpressure control valve 110 with the extension rod 111 that is describedabove and illustrated in FIG. 5, and the brake pedal 1 with a push rod118 opposing to and spaced by a predetermined gap G away from theextension rod 111. Although the stroke sensor 120 is applied to thebrake pedal 1, other sensors for detecting the stepping force may beinstalled thereto. Other structures are similar to those of theembodiment illustrated in FIG. 5.

In the operation of the vehicle brake system of the embodiment soconstructed, once the driver steps the brake pedal 1, the stroke sensor120 detects the stroke thereof and then outputs the signal in responseto the stroke to the control device 70. The control device 70 activatesthe proportional pressure control valve 110 in accordance with theoutput signal so as to guide the pressurized braking liquid stored inthe accumulator into the wheels. This operation is similar to that ofthe conventional brake system. According to the embodiment of thevehicle brake system, the stroke corresponding to the predetermined gapG causes the push rod 118 to contact with the extension rod 111, and thefurther stroke beyond the predetermined gap G presses down the extensionrod 111. The downward press of the extension rod 111 also presses downthe spool 52, and actuates the proportional pressure control valve 110so that the input port 41 has a larger opening. Thus, since theproportional pressure control valve 110 is controlled both directly bythe operation of the brake pedal 1 and by the signal output in responseto the stroke from the stroke sensor 120, the more effective brakingforce can be obtained with use of the high pressure of the brakingliquid stored in the accumulator 36.

Although the embodiment of the present invention illustrated in FIG. 8is applied to the prior art brake system shown in FIG. 14, it is notlimited thereto, and it may also be applied to any types of vehiclebrake systems such as one shown in FIG. 12. Also, FIG. 8 shows theseparate extension rod 111, however, the sleeve may have an extensionportion extending through the hole, on which the push rod 118 pressesdownwardly. According to the embodiment, advantageously, theproportional pressure control valve 110 can be actuated in theoff-powered condition, and the safety can be improved in emergency.

FIGS. 9( a) and 9(b) show various modifications of the embodiment,illustrating a portion above the imaginary line X-X in FIG. 8. Otherstructures not shown are similar to those in FIG. 8. In FIG. 9( a), theextension rod 111 is eliminated, and the push rod 118 of the brake pedal1 is positioned so that it opposes to the spool 52 with thepredetermined gap G therebetween. The operation of the modification issimilar to that described above and illustrated in FIG. 8 except thatthe push rod 118 itself directly presses down the spool 52 after thebrake pedal is stepped beyond the predetermined stroke. Also, an elasticmember such as a spring may be intervened in the gap G in FIGS. 8 and 9(a). In this case, the operation of the brake pedal compresses thespring, which in turn, biases the spool 52 downwardly. As the spring iscompressed, the biasing force to press the spool 52 down is increased,this advantageously causes the proportional pressure control valve 110to be controlled in response to the stroke of the brake pedal stepped bythe driver.

In FIG. 9( b), provided in the upper and inner portion of the sleeve 51a is a reduced bore portion defining a step. Also, a stop plate 115 anda spring 119 are positioned in contact with and between the step and theupper surface of the spool 52. The push rod 118 a connected with thebrake pedal 1 is biased upwardly by a return spring so that it definesthe gap G to the stop plate 115. When the brake pedal 1 is steppedbeyond the predetermined stroke, the push rod 118 a contacts with thestop plate 115, and then compresses the spring so as to press the spooldownwardly. Since the spring more compressed generates the strongerbiasing force to press the spool 52 down, the modification in FIG. 9( b)has the advantage similar to that in FIG. 9( a). In addition to this,conveniently, the spring 119 serves as a buffer.

According to the modifications illustrated in FIGS. 9( a) and 9(b), theproportional pressure control valve 110 can be controlled not only bythe control device 70 but also by the stroke of the brake pedal 1. Itshould be noted that the elastic member shown in FIG. 9( b) may be arubber strip instead of spring 119.

In another modification of the embodiment, the embodiment of the presentinvention can be applied to the vehicle brake system described above andillustrated in FIG. 5 of the above-mentioned embodiment. In particular,although the electromagnetic clutch 113 holds or grasps the extensionrod 111 in the off-powered condition such as in emergency, it may alsobe used in the powered condition to hold the extension rod 111 if thestroke sensor 120 detects the signal indicating that the brake pedal isstepped beyond the predetermined stroke. To this end, the proportionalpressure control valve 110 is controlled only by the control device 70while the stroke of the brake pedal is within the threshold value,however when it exceeds the predetermined value, the electromagneticclutch 113 is actuated to allow the brake pedal operation to directlycontrol the proportional pressure control valve 110. The advantages ofthe modification is similar to that described above for the embodiment.

Next, with reference to the drawings, a sixth preferred embodiment of abrake system for automobiles according to the present invention will bedescribed in detail. FIG. 10 is a graph illustrating the relationshipbetween a stroke of the brake pedal stepped by the driver and thepressure of the braking liquid generated within the master cylinder 2.When the driver steps the brake pedal, the piston within the mastercylinder moves and then the braking liquid therein is pressurized.However, in particular, when a drum brake is utilized for braking thewheels, the pressurized braking liquid has to move a wheel cylinderpiston provided with the wheel to some distance so that the brakingliquid pressure is not increased so much. Also, when a disk brake isutilized, while the pressurized braking liquid moves a pad of a caliper,the braking liquid pressure is not increased so much. Thus, once the padactually contacts with the brake disk or drum, the braking liquidpressure serves as a force pressing the drum or disk, and then increasesremarkably. This is because the braking liquid itself can not beconstricted, and the passage, the cylinder, and the flexible hose hardlyexpand due to the braking liquid pressure, and also the brake pedal armis little bent when stepped by the driver. To this end, as illustratedin FIG. 10, there is the relationship between the stroke of the brakepedal and the braking liquid pressure, in which the slope of the brakingliquid pressure is gentle up to the stroke point a, and is steepthereafter.

In the conventional brake system, once the control device 70 receives aninput signal representative of the pressure of the braking liquid withinthe master cylinder as shown by the real line in FIG. 10, it controlsthe current applied to the coil 62 of the control portion 60 that isproportional to the liquid braking pressure. Contrary, according to theembodiment, the input signal representative of the stroke instead of thepressure is applied to the control device 70, which, in turn, suppliesthe current to the coil 62 corresponding to the input signal so thatmore appropriate braking force can be obtained in response to the pedalstroke stepped by the driver.

Therefore, in the embodiment of the present invention, the controlportion controlling the proportional pressure control valve 80 receivesthe input signal representative of the stroke, rather than the brakingliquid pressure within the master cylinder used in the foregoingembodiments illustrated in FIGS. 2 through 9. This can be realized byproviding a stroke sensor 120 with the brake pedal 1 as shown in FIG. 1,which detects the stepped stroke of the brake pedal 1 to output thesignal as indicated by the dashed line in FIG. 10 to the control device70.

Also, referring to FIG. 10, the braking liquid pressure in response tothe linear output signal based upon the stepped stroke has the samepressure as that within the master cylinder at the stroke point b, andthe latter is higher than the former beyond the stroke point b. In otherwords, once the braking liquid begins to press the braking drum or diskso as to brake the wheel, a small increment of the stroke significantlyincreases the pressure of the braking liquid. Meanwhile, for examplewhen required to halt the wheel in emergency, advantageously, thebraking liquid pressure may be much higher than that corresponding tothe output signal shown by the dashed line. In order to incorporate theadvantage with the embodiment, the control device 70 receives the inputsignal such that the braking liquid pressure linearly increases up to oradjacent to the stroke point b, and increases corresponding to thepressure of the braking liquid within the master cylinder beyond thestroke point b.

Therefore, according to the embodiment, the control device 70 outputsthe instruction regarding to the current supplied to the coil 62 in thevalve control portion 60 of the proportional pressure control valve 80such that the instruction is defined based upon the combination of thestroke of the brake pedal 1 and the braking liquid pressure, thus forachieving the more appropriate braking force. In order to realize this,input to the control device 70 is the signal indicating the strokedetected by the sensor 120 shown in FIG. 1 or the pressure of thebraking liquid sensed within the master cylinder 2, and the controldevice 70 is provided with a logic circuit for selectively switching thesignal corresponding to the stroke or the braking liquid pressure.

Although no description is made for other brake systems such as the ABSand the traction control, this invention results in no adverse impact tothose systems, on the contrary, it can be utilized in cooperationtherewith.

According to the vehicle brake system of the present invention, thepressurized braking liquid stored in the auxiliary pressure source canbe exploited even when the electric system fails in emergency as well asin normal powered condition without any undue load for the driver so asto ensure the sufficient braking force to be applied to the wheels evenin the off-powered condition.

Also, according to the present invention, the addition of the simplefeature to the braking system itself incapable of braking the wheels inthe off-powered condition allows the pressurized braking liquid storedin the auxiliary pressure source to be exploited even when the electricsystem fails in emergency as well as in normal powered condition withoutany undue load for the driver so as to ensure the sufficient brakingforce to be applied to the wheels even in the off-powered condition.

Further, according to the present invention, the more effective brakingforce can be obtained by increasing the movement of the proportionalpressure control valve in a condition where the brake pedal is steppedbeyond the predetermined stroke in the normal powered condition. Inaddition, even in the off-powered condition such as in emergency, theproportional pressure control valve can be controlled so that the safetyof the brake system can advantageously be improved in emergency.

Even further, according to the present invention, the brake system usedfor the automobiles can be controlled both by the braking liquidpressure and by the stroke of the brake pedal so that the moreappropriate braking force can be ensured in accordance with the brakepedal operation.

1. A braking system comprising: a brake pedal; a stroke sensor thatoutputs a stroke signal in response to a stroke of the brake pedal; anaccumulator that accumulates a pressurized braking liquid; aproportional pressure controller that controls the pressure of thepressurized braking liquid, and supplies the pressurized braking liquidto a wheel, the proportional pressure controller including a spool and astop plate movably supported at one end of the spool by an elasticmember; and a push rod connected to the brake pedal and movable betweena first position spaced from the stop plate and a second positioncontacting the stop plate, wherein the push rod moves in response to thestroke of the brake pedal in order to contact and push the stop plate tothereby move the spool; wherein the proportional pressure controllercontrols the pressure of the pressurized braking liquid in accordancewith the stroke signal and the motion of the push rod during anon-powered condition, and in accordance with only the motion of the pushrod during an off-powered condition.
 2. The braking system according toclaim 1, wherein the proportional pressure controller includes anopening through which the push rod extends, and a sealing member locatedin the opening for sealingly engaging the push rod in the opening. 3.The braking system according to claim 2, wherein the push rod is biasedin a direction away from the proportional pressure controller by aspring.
 4. The braking system according to claim 1, wherein the elasticmember is a spring positioned between the one end of the spool and thestop plate.